Telephone system



H. HQVLAND TELEPHONE SYSTEM 2 Sheets-Sheet; 1

Filed Jan. 17, 1941 II n . INVENTOP H. HOVLANDv Sept. 8, 1942.-

5555; zokumkiou E ATTORNEY P 1942- H. HOVLAND 2,294,907

' TELEPHONE SYSTEM Filed Jan. 17, 1941 2 sheets-sheet 2 INVENTOR H. HOVLAND w $63 v w .336 1 .386 E85 #3 E25 kwmt E55 .53

w wt w wt Patented Sept. 8, 1942 TELEPHONE. SYSTEM Henry Hovland, Williston Park, N. Y., assignor to Bell Telephone Laboratories,

Incorporated,

New York, N. Y., a corporation of New York Application January 17, 1941, Serial No. 374,822

8 Claims.

This invention relates to telephone systems and more particularly to systems employing automatic switches for establishing conversational connections.

An object of this invention is to provide a more economical allotting arrangement of finder switches. Another object is to simplify the linefinder circuits by reducing the amount of electromagnetic apparatus required to a minimum without sacrificing any of the desirable operating features.

In accordance with this invention, the line finders of a group of finders are allocated sequentially by contact springs of off-normal switches associated with each finder, the normal contact springs thereof connecting the start circuit of a calling line to its own idle finder; and the ofinormal contact springs, after the finder has operated, extending the start circuit for a subsequent calling line of the same group to the normal contact springs of a corresponding switch of another idle finder of the same group. Once a finder has operated, it cannot release immediately after a subscriber has disconnected but must remain in the actuated position until all finders in the group have functioned. The free finders then release and reoperate as required. However, should all finders of a group be engaged at any moment none can release, and a chain circuit connects the start circuit to another group of finders.

A feature of the invention resides in a linefinder circuit having a vertical off-normal switch in which contact springs are actuated by the initial vertical movement of the shaft and held in the actuated position until all finders of a group of finders are in the operated state.

Another feature resides in a line-finder circuit all finders of said group have operated and wherein all finders of one group being engaged at one time, the start circuit for a subsequent calling line'is extended to another group of find- BIS.

Other features of the invention relate to circuit improvements which will be apparent from the following detailed description of the drawings comprising Figs. 1, 2 and 3, which show by means of the usual circuit diagrams a sufficient amount of apparatus to enable the invention to be described and understood.

The invention is illustrated in a system using step-by-step line-finder switches each having a capacity of two hundred lines, and each having two sets of wipers; but the invention is not limited in its application to the specific arrangement shown.

Referring to the drawings:

Fig. 1 shows schematically calling subscribers stations A and B, placed in one group, corresponding line and start circuits, 2. chain circuit for transferring the start circuit from one group to another during an all-busy period of one group, a finder circuit, selector circuits, a connector, and a called subscribers substation;

Fig. 2 shows the last finder of group I in skeleton outline; and

Fig. 3 shows the finders of group 2 in skeleton outline with the start circuit sequentially connected through the ofi-normal contact springs of the finder switches as embodied in this invention.

The subscribers stations are of the type usually employed in automatic telephone systems and each includes a dial for use in obtaining connections with, any other station. Each station connects at the exchange with a line circuit comprising a, two-step combined line and cut-off relay, which actuates partially when the subscriber initiates a call and fully when the finder seizes the calling line. Each line circuit is assigned to a certain group and for illustration purposes substations A and B have been allotted to the same group, with subscriber A occupying the upper bank and subscriber B, the lower bank of the same level. The line-finder, selector, and connector switches are of the well-known twomotion step-by-step type.

In order to reduce the cost of the line-finder circuit, applicant has provided his line-finder circuit with a minimum of electromagnetic relays and he has accomplished this in general by the use of contacts on double-dog and vertical offnormal switches. In addition, the line-finder and change-over relays have been combined into a single two-step relay. Applicants system is also arranged to prevent the release of any finder switch until all switches of a group have oper- 5 ated, thereby assuring continuity for a start circuit after it has been sequentially connected through the off-normal contact of an operated finder switch to the normal contact of a free finder switch.

The invention will be most readily understood from a detailed description of the operation.

Assuming a call to have been originated at subscribers station A, a circuit is closed upon removal of the receiver, which energizes two-step combined line and cut-off relay Hi3 in its first step as follows: from ground through the lower winding of relay I03, back contact thereof, over conductor IOI through the substation loop, back over conductor I02, and thence through back contact and upper winding of relay I03 to battery. Two-step relay I03 operates in its first step to close the upper front contacts a and 1), none of the normally closed contacts opening. At the uppermost front contact negative battery potential is connected from the middle winding of relay I03 in parallel to bank terminal I04 to mark the line of station A as calling and to the connector multiple; and at upper intermediate front contact connects ground to the No. 1 vertical bank contacts of commutator segments I28 of the same group and also completes a circuit by way of resistance I06 and common start conductor I20 through the winding of start relay I I9 to battery. It will be noted that the vertical commutator bank I28 of one group of finders is slip multipled in the customary manner to the vertical commutator bank 228 of the other group of finders.

Relay II9, upon energizing, at its right front contact provides an operating circuit for the combined finder start and change-over relay I23 by connecting ground through the left front contact of normally operated chain relay I2I, thence through normal contact of VON switch I26, resistance I24, and to battery through the lower winding of relay I23. Relay I23 is also a twostep relay and upon energization in its first step closes the four contacts 0, d, e and f. The uppermost front contact prepares a holding circuit for electropolarized relays II! and H8 while the upper inner front contact prepares a holding circuit for relay I23 and also an operating circuit for the vertical and rotary magnets. Ground at the lower second intermediate front contact of relay I23 provides an obvious holding circuit for chain relay I2I, which is normally held operated by ground at the lower normal contact of VON switch I26.

The closing of the lower first intermediate front springs of relay I23 provides a circuit from battery through winding of vertical stepping magnet I08, normal back contacts of relay I23, vertical magnet I08, and rotary magnet I09, respectively, thenc through front contact of relay I23, normal contacts of 10th rotary step springs I21 and VON switch I26 and through left front contact of chain relay I2I and front contact of relay I I9 to ground. Vertical magnet I08 operates and begins to step the shaft (not shown) and brushes of the finder LF up to the first level of the vertical commutator bank I28. However, magnet I08 attracts its own armature and thereby opens the circuit; but the shaft, while it is being elevated, causes the double-dog springs M to close and short-circuit the springs of the vertical magnet I08. The vertical magnet, therefore, remains energized until the shaft has taken a full step, after which the double dog drops into a ratchet (not shown) of the shaft, separates its springs I I6 and thereby opens the circuit of vertical magnet I08.

Magnet I03 releases its armature, which reclose's the above-traced circuit for another stepping operation. This automatic stepping continues to the level in which the calling line is found.

As soon as the shaft of the finder switch is moved out of its normal position, the VON switch I26 is actuated and thereby disconnects ground at its lower contact spring from chain relay I2I. Relay I2I, however, remains energized through ground at relay I23 in an obvious circuit already mentioned. The actuation of VON switch I26 also prepares at its uppermost contact a circuit for release magnet I01 and at its intermediate contact transfers the previously mentioned start circuit from the normal to the off-normal spring so that the operating circuit for relay I23 and magnet I08 becomes as follows: ground from right front contact of relay I I9 through left front contact of relay I2I, off-normal contact of VON switch I26, front contact of relay I23, through upper back contacts of relays Ill and H8, and thence in parallel legs, one leg of the circuit continuing through lower front contact of relay I23, normal contact of 10th rotary step springs I21, and through resistance I24 and lower winding of relay I23 to battery; and the other leg through contact of double-dog springs II6, lower back contact of relay I23 and winding of vertical stepping magnet I08 to battery. During the actuation of the VON switch I26 neither vertical stepping magnet nor finder relay I23 releases as the off-normal spring of the switch makes before the normal spring breaks thus preservin continuity of the circuit.

When the level of the calling line is reached by the vertical switch (in this case it has been assumed as at the first level), ground on commutator segment I of vertical bank I28 is connected by vertical wiper I29, through upper winding of relay I23, normal back contact of release magnet I01, lower back contact of relay I23, thence through winding of vertical magnet I08 to battery. Vertical magnet I08 remains operated in this circuit until two-step relay I23 fully operates in its final step, after which relay I23 at its lowermost springs transfers the stepping operation from the vertical to the rotary phase, and at its upper two front contacts prepares operating circuits for relays H1 and H8. In fully operating relay I23 also provides itself with a locking circuit from battery through its lower winding and lower inner front contact, normal contact of 10th rotary step springs, lower front contact of relay I23, upper back contacts of relays H0 and 1, upper front contact of relay I23, off-normal contact of VON switch I26, left front contact of relay I2I, and to ground through front contact ofrelay II9. Vertical magnet I08 releases andgrotary magnet I09 operates in acircuit from battery through its own winding, lower front' contact of relay I23; back contacts of vertical magnet I08 and rotary magnet I09, thence through upper back contacts of relays H8 and [[1, upper front contact of relay I23, off-normal contact of VON switch I26, left front contact of relay I2I,

and front contact of relay II9 to ground. As inthe vertical stepping operation the double-dog switch contact II6 cooperates with the rotary magnet to advance the rotary brushes successively from one set of terminals to the next until the terminals of the'dialing line are found.

When brush I 05 makes contact with sleeve terminal I04 of the calling line, electropolari'zed relay' I I! operates in a circuit from battery through the middle winding and upper front contact;

of relay I03, sleeve terminal I04, brush I05, lower (primary) winding of relay I II, and throughupper front contact or relay I23 to ground. This circuit is also effective to fully operate twostep combined line and cut-off relay I03. Relay II! is so designed that when operated over the primary winding it will remain operated over the secondary or polarized winding in a circuit from battery through upper (secondary) winding of relay 1, lower back contact of relay H8, and thence through upper front contact of relay I23 to ground. The operation of relay [I1 ex: tends the tip and ring line conductors Hitand I02 through its upper front contacts to the associated selector circuit S, also causes the release of relay I23, and prevents further operation of rotary magnet I08 by opening the start conductor at its upper back contact. Relay I23, however,"

is slow in releasing and maintains aground on the sleeve until ground has been returned from the selector circuit S. Ground from selector S provides a holding circuit for relay III over sleeve conductor I25, through lower inner, back contact of relay I I8 and upper (secondary) winding of relay II! to battery. The call thenproe ceeds through selector SI and connector dto the called substation L in the customary manner.

The combined line and cut-off relaylfifi, having fully operated, removes ground from the tip conductorIBl and battery from the ring conductor I02, and disconnects ground from the vertical commutator bank" I28 and start, con ductor I20, thereby releasing start relay H9 for use with other calling subscribers of the same groupsuch as subscriber B. Upon the release of relay I19 ground for relay I23 is removed but this has little efiect on relay I23 as relay II! has already opened the operating circuit for relay I23. With brush I in contact with sleeve terminal I04 of the line of substation A, the potential of the sleeve terminal of this line in the banks of all line finders and connector switches having access thereto will indicate that the line is busy and as a result will prevent any other hunting line finder or any connector switch from stepping on the terminals of this line.

No further operation takes place in the linefinder circuit until the connection is released by the calling subscriber at which time the selectors and connector through which the connection was completed are restored to normal, and the holding ground is disconnected from sleeve conductor I25. Combined line and cut-off relay I03 is thereby released so that another call may be initiated, or an incoming call received, at substation A. Relay I I! also releases when the holding ground is disconnected from sleeve conductor I25.

With the disconnection of a call between substations A and L the line-finder circuit LF would be free for another call under normal circumstances but the system shown herein does not permit the release of the finder switch until all finders of the group are in an operated position. When this condition is satisfied, chain relay I2I releases and connects operating ground for release magnet I01, which returns all free finder switches to normal, the engaged finders necessarily remaining in the operative position.

Let it be assumed, for example, that all line finders of group I as shown in Figs. 1 and 2 are in use and that calling substation A, the last in the group, has just established his connection with selector S. As described earlier, relay I23 being a slow-release relay releases after ground 21 operating circuit for chain relay I2I.

the group are actuated and their associated VON switches are in off-normal positions, chain relay I2I releases and provides an operating circuit magnetlq'l, uppermost contact or VON switch. I26, thencethroughlower back contacts of.re-,'-'

lays I I8 and I I7 and winding of release magnet I01 to battery. Release magnet I01 operates and provides itself with a locking circuit from ground.

at its left front contact through the uppermost contact of VON switch I20, back contacts of relays IIS and II] to batterythrough winding of magnet I0]. Magnetlfil remains operated until the finder switch returns to normal. after which the circuit is opened at the uppermost contact of VON switch I20. Magnet I01 having released and VON switches I26 of all free finders having returned to their normal positions, chain relay I2I reoperates in a circuit from, ground at the lower back contact of a VON 7 switch I26, through resistance I22 and winding of relay I2I to battery. Relay IEI thus places all free finders in readiness for succeeding calls.

, The above example describes u the condition where after all finders of a group had operated and the chain relay had released, free finders were available for further calls. Let it next be assumed that all finders of the group have operated and the chain relay has released but that no finder is free for any succeeding call. Assuming that a, call is started at substation A, the combined line and cut-01f relay I03 operates as described before and causes the start relay II9 to operate. Since chain relay I2I has released and cannot reoperate because of lack of free finders in its group, ground at the right front contact of relay H9 is transferred to the finders of group 2 through the outer left back contact of chain relay I2I over conductor I30, thence through the left front contact of chain relay 22I for group 2, normal contact of VON switch 220, resistance 224, to battery through winding of relay 223. Finder relay 223 operates and repeats the operating procedure already described following the operation of relay I23 of group 1.

What is claimed is:

1. In a telephone system, a group of lines, a group of finders having access to said lines, the finders of said group of finders arranged in sequence to serve said lines in a definite order, each of said finders having a set of switching contacts operable in response to the movement of the finders, a start circuit common to said finders, means including the switching contacts of the first idle finder in the group for extending said start circuit to said idle finder, means responsive to a call on one of said lines for closing said start circuit to operate said idle finder, the switching contacts of said operated finder serving to extend said start circuit to the next finder in the group, means for releasing said finders, and means for preventing the release of After an' operated finder until all finders in the group are operated.

2. A telephone system according to claim 1, and means responsive to the operation of the last finder of said group for releasing all free finders to their normal positions.

3. In a telephone system, a group of subscribers lines, a group of finders having access to said lines, the finders of said group of finders arranged in sequence to serve said lines in a definite order, each of said finders having an off-normal switch operable in response to the movement of the finder, a start circuit common to said finders, means including a normal contact of said switch of the first idle finder in the group for extending the start circuit to said idle finder, means responsive to a call on one of said lines for closing said start circuit to operate said idle finder, an ofi-normal contact on said switch of said operated finder serving to extend said start circuit to the next finder in the group, means including a relay and ofi-normal contact of said switch for releasing said finders, and means including a normal contact of said switch of a free finder in the group for preventing the release of an operated finder until all finders in the group are operated.

4. A telephone system according to claim 3, and means responsive to the operation of the last finder of said group for releasing all free finders to their normal positions.

5. A telephone system according to claim 3, and means including a relay responsive to the operation of the last finder of said group for releasing all free finders to their normal positions.

6. In a telephone system, a plurality of groups of subscribers lines, a finder group for each of said groups of lines, the finders of each of said groups of finders arranged in sequence to serve said lines in a definite order, each of said finders having a set of switching contacts operable in response to the movement of the finder, a start circuit common to each of said finder groups, means including the switching contacts of the first idle finder in each of said groups for extending said start circuit to said idle finders, means responsive to a call in each of said subscriber line groups for closing said start circuit to operate said idle finders, the switching contacts of said operated finders serving to extend said start circuits to the next finder in their respective groups, means for releasing said finders, and means for preventing the release of the operated finders of any group until all finders in said group are operated.

7. A telephone system according to claim 6, and means responsive to the operation of the last finder of any group of finders for releasing all free finders in said group to their normal positions.

8. A telephone system according to claim 6, means responsive to the operation of the last finder of any group of finders for releasing all free finders in said group to their normal positions and also for transferring said start circuit from one group of finders having all finders engaged to another group of finders having free finders available for further service.

HENRY HOVLAND. 

